The present embodiments relate to an arrangement for processing a non-symmetrical signal. The arrangement includes an apparatus for balancing and filtering an image frequency of a nominal frequency of the non-symmetrical receiving signal. The present embodiments further relate to an arrangement for processing a signal balanced to ground.
The apparatus for balancing transforms a real impedance balanced to ground into a real impedance balanced to ground for a specific nominal frequency and/or a defined frequency range about the nominal frequency. The problem of balancing and suppressing a higher frequency in the vicinity of the nominal frequency or a lower frequency (i.e., a so-called image frequency) in the vicinity of the nominal frequency usually occurs with receivers having a mixer that multiplies a receiving frequency with the frequency of a local oscillator. The image frequency is unwanted with respect to any further processing and should, therefore, be suppressed.
On account of the principle of reciprocity, this problem also applies in the reverse direction, when, for example, mixing a non-symmetrical signal during transmission.
Two different functional blocks were previously used to balance and suppress an image frequency. The balancing was effected by a balancing unit such as a Boucherot bridge. A filter is used to fade-out the unwanted frequency. Using two separate functional blocks, however, results in a high outlay in components, such that the receiver needs a larger installation space.
Balancing and filtering may also be combined using so-called SAW (surface acoustic wave) filters (also known as surface wave filters). Such filters are, however, very expensive for custom-made products, particularly for products, such as medical devices, with a small number of pieces. Magnetically coupled dual circuit band filters may also combine both functions, but for image frequencies in the vicinity of the receiving frequency, high quality coils, i.e., coils with a large design, are used and the degree of magnetic coupling must be precisely known, both of which are disadvantageous in practice.